The present invention relates to a phosphor screen with metal back, a forming method thereof and an image display device having the phosphor screen with metal back.
Conventionally, a face plate of a cathode-ray tube (CRT) or an image display device of a field emission type (FED) has a metal back layer of aluminum (Al) or the like formed on a phosphor layer, which is disposed on the internal surface of a translucent panel, by a method such as vacuum deposition. The metal back layer reflects light advancing in a direction of an electron source, which is in the light emitted from the fluorescent material (phosphor layer) by electrons emitted from the electron source, to the panel side to enhance brightness and also serves to stabilize the potential of the phosphor layer. It also has a function to prevent the phosphor layer from being damaged by ions generated by ionization of residual gas in a vacuum envelope.
Generally, the FED has a lower electron beam acceleration voltage of 500 V to 10 kV than that of the CRT and a higher current value than that of the CRT, to make the fluorescent material to emit light. Therefore, there was a phenomenon referred to as so-called film deterioration that emission brightness of the phosphor layer is lowered substantially by the continuation of the electron beam irradiation.
One of the causes of the deterioration of such emission brightness is considered to be the accumulation of electric charges generated by the electron beam irradiation in the phosphor layer. And, it is known as shown in FIG. 8 for example that brightness can be improved by forming a metal back layer of aluminum on the phosphor layer as compared with the case without the metal back layer. And, an effect of suppressing the deterioration of emission brightness by such a metal back layer is substantially not variable depending on the thickness of the aluminum film. Electron beam irradiation conditions in FIG. 8 are to perform spot fixed continual irradiation to a phosphor layer at an anode voltage of 6 kV and a cathode current of 150 xcexcA/cm2 and measure brightness in a degree of vacuum of 10xe2x88x925 Pa.
A conventional metal back layer, however, does not have a sufficient effect of suppressing the deterioration of emission brightness, and brightness is lowered because an electron beam is partly absorbed by the metal back layer. Thus, a phosphor screen which maintains high brightness for a long time could not be realized.
The present invention has been completed to remedy the above problems, and an object of the invention is to provide a phosphor screen with metal back which substantially suppresses the deterioration of emission brightness of the phosphor layer, a method for forming it, and an image display device which has the phosphor screen with metal back improved in the brightness and can make display of high brightness.
A first aspect of the present invention is a phosphor screen with metal back as described in claim 1, which comprises a phosphor layer formed on the internal surface of a translucent substrate and a metal back layer formed on the phosphor layer, wherein a degree of adhesion of the metal back layer to the phosphor layer is 30% or more in a ratio of areas of the layers contacted with each other.
As described in claim 2, the phosphor screen with metal back of the present invention can have the metal back layer with a thickness of 5 to 100 nm, and the light transmittance of 10% or less. And, as described in claim 3, the metal back layer can have an intervening layer containing inorganic particles on at least one main surface thereof.
A second aspect of the present invention is a method for forming a phosphor screen with metal back as described in claim 4, which comprises preparing a translucent substrate, forming a phosphor layer on the internal surface of the translucent substrate, forming a metal back layer, the forming of the metal back layer including disposing a transfer film having a base film and at least a parting agent layer and a metal layer stacked on the base film so that the metal layer is contacted to the phosphor layer with an adhesive agent layer between them, transferring the metal layer by pressing and bonding, and peeling the base film, and heating the substrate which has the metal back layer formed on the phosphor layer, wherein the metal layer is transferred in such a way that a degree of adhesion between the phosphor layer and the metal layer is 30% or more in a ratio of areas of both the layers contacted.
As described in claim 5, the method for forming the phosphor screen with metal back according to the present invention can have a step of forming an intervening layer containing inorganic particles on the phosphor layer before disposing the transfer film on the phosphor layer in the step of forming the metal back layer. As described in claim 6, the method for forming a phosphor screen with metal back can further comprise forming an intervening layer containing inorganic particles on the metal back layer formed on the phosphor layer after heating the substrate.
A third aspect of the present invention is an image display device as described in claim 7 and the image display device has a face plate, wherein the phosphor screen with metal back as set forth in claim 1 is disposed on the face plate. And, as described in claim 8, this image display device can comprise a rear plate being disposed opposite to the face plate and have many electron-emitting elements on the rear plate.
In the phosphor screen with metal back according to the present invention, a degree of adhesion between the metal back layer and the phosphor layer is increased to 30% or more in the ratio of areas of both the layers contacted to each other as compared with prior art, so that the deterioration of emission brightness of the phosphor layer is suppressed substantially. To form such a phosphor screen with metal back having a high degree of adhesion between the metal back layer and the phosphor layer, the metal back layer having a very low light transmittance, namely high reflectivity, can be obtained by adopting the transfer method, and an image display device capable of making highly bright and high-definition display can be obtained.